Montgomery Ward & Co., the nation's sixth-largest retailer, has reported a 33 percent increase in 1984 earnings over the previous year to $53 million, and sales of $6.468 billion, up 8 percent.

Ward's fourth-quarter net earnings of $69 million represented a 30 percent jump over the same period in 1983, while sales of $2.13 billion represented a 2 percent increase, the company said Thursday.

Ward's outperformed Mobil Corp., its parent firm, on a percentage basis.

Ward's yearly earnings were less than its fourth-quarter earnings because of a $16 million loss during the first nine months of 1984, a company spokesman said.

Shell Oil, the nation's seventh-largest oil company, said its profit rose 5.8 percent in the fourth quarter and increased 8.5 percent for all of 1984, reaching record highs for both periods.

Much of the gains came from outside the operations of Shell's oil business, including tax benefits and lower interest expenses.

For the final three months of the year, earnings rose to $581 million ($1.88 a share) from $549 million ($1.78) for the same period a year earlier, when the previous record was set. Revenue edged up to $5.27 billion from $5.25 billion.

Fourth-quarter earnings more than quadrupled to $101 million from $25 million from such unallocated corporate items as lower interest expenses, higher interest income and a tax adjustment applicable to prior years.

For all of 1984, profit rose to $1.77 billion ($5.73) from $1.63 billion ($5.28) in 1983. The previous record for annual earnings of $1.70 billion was set in 1981.

Revenue rose 5.1 percent to $20.90 billion from $19.88 billion. McDonnell Douglas Corp. yesterday reported 1984 earnings of $325.3 million ($8.10 a share) compared with earnings of $274.9 million ($6.91) the previous year. Sales for 1984 were $9.66 billion compared with $8.11 billion in 1983.

Fourth-quarter 1984 earnings were $91.7 million ($2.28) on sales of $2.62 billion compared with $82.6 million ($2.07) on sales of $2.06 billion in 1983 period.